August 21, 2019
Authored by Jeff Fecteau, Senior Regulatory Engineer
When the 2017 National Electrical Code (NEC) became available in October 2016, it contained a new Article 706 covering energy storage systems (ESS). Section 706.1 states that the provisions of Article 706 apply to all permanently installed ESS operating at over 50 volts ac or 60 volts dc that may be stand-alone or interactive with other electric power production sources. Additionally, Section 706.5 requires that ESS components be listed and if the ESS is self-contained system, it must be listed as a complete ESS.
Fast forward to the 2020 NEC in which several code proposals were accepted by code making panel 13 (CMP 13) to expand the scope of Article 706 to include all ESS, not just permanently installed systems. Article 706 was also changed to include ESS with a voltage capacity rating greater than 1 kWh. These code proposals identified that Article 706 was unnecessarily limited to permanently installed ESS in recognition that temporary applications such as concerts, festivals, disaster relief, etc., all have the same potential fire and shock hazard as permanent systems. The proposals acknowledged that from a U.S. electrical safety point of view, the electrical safety requirements are very similar for both permanently and temporarily installed ESS.
Also, Section 706.5 has been revised to simply state that ESS are to be listed. This is a significant change because now an ESS must be listed as a complete energy storage system and is no longer permitted to be made up of a field assembly of listed components.
UL Certified ESS include a UL Certified Mark
ESS certified by UL are covered by UL product category Energy Storage Systems and Equipment (FTBW). The basic Standard used to investigate products in this category is UL 9540, the Standard for Safety of Energy Storage Systems and Equipment. Energy storage systems may be standalone, utility interactive or multimode. Standalone systems are intended to operate independently of the utility grid. Utility interactive systems operate in parallel with the utility grid. A multimode systems can operate as both or either a standalone system (utility independent) or as a utility interactive system. For multi-piece units, the UL Certification Mark appears on the outside of each enclosure section constituting a complete energy storage system eligible for certification. The Certification Mark covers only the enclosure section to which it is affixed; it does not cover other enclosure sections included in the system. Each enclosure section of a UL Certified energy storage systems includes a notation identifying the total number of enclosure sections in the certified system and the specific enclosure bearing the Certification Mark (Section _____ of _____ marking). The second blank indicates the total number of enclosure sections contained in the certified energy storage system and the first blank indicates the respective enclosure section number bearing the Certification Mark.
Markings and Installation Instructions
Energy storage systems are factory or field-wired assemblies in which the combination has been investigated for operation as a system assembly when installed in accordance with the manufacturer's installation instructions. Both NEC Section 706.4 and UL 9540 require that the ESS be provided with a nameplate plainly visible after installation and marked with the following:
- Manufacturer’s name, trademark or other descriptive marking to identify the organization responsible for supplying the ESS
- Rated frequency
- Number of phases, if ac
- Rating (kW or kVA)
- Available fault current derived by the ESS at the output terminals
- Maximum output and input current of the ESS at the output terminals
- Maximum output and input voltage of the ESS at the output terminals
- Utility-interactive capability, if applicable
The 2020 NEC Article 706 now applies to both permanently and temporarily installed ESS larger than 1 kWh. Section 706.5 no longer permits listing of individual components but instead requires that the complete ESS be listed. These revised requirements will assist authorities having jurisdiction (AHJs) with inspecting and approving ESS. As an example, NEC Section 90.7 identifies that inspection of factory-installed internal wiring or the construction of equipment at the time of installation is unnecessary if the equipment has been listed by a qualified electrical testing laboratory such as UL.
Because the requirement for a complete ESS listing is new, a code authority or AHJ may encounter an ESS that does not bear the listing mark required by the NEC. Should this happen, UL may be able to assist by conducting a field evaluation of an installed ESS. However, UL 9540 may contain some functionality requirements that cannot be adequately evaluated in the field. If the UL field evaluation determines that the ESS is compliant with UL 9540, a UL Field Evaluated label is affixed to the ESS. This meets the NEC requirement for a listed ESS, and an AHJ can base acceptance on the UL Field Evaluated label and the written report.
For more information, please contact [email protected].